The luminescent composition consisting essentially of aluminum oxide activated by chromium is well known. This composition gives a line emission in the deep red. Line-emitting phosphors have been found useful in a number of applications. In U.S. Pat. No. 3,772,099, dated Nov. 13, 1973, issued to Ryan et al and assigned to the present assignee is disclosed the use of line-emitting phosphors for providing a distinctive information label for identifying explosives. A predetermined combination of line-emitting phosphors can be used as "coding" phosphors which provide a very individualistic emission when excited by predetermined energy such as ultraviolet radiation. These coding phosphors can provide post-explosion information as to the origin, date of manufacture, and type of explosive used.